1. Field of the Invention
This invention relates to joint replacement prostheses for the knee, and more particularly to such prostheses that can be implanted by minimally invasive surgical techniques.
2. Brief Description of the Prior Art
Replacement of diseased or damaged knees with suitable prostheses has become a common surgical procedure. The outcome of such surgery has been found to be favorable in most cases, and the surgery has come to be regarded as a very favorable surgical intervention for restoring function to knees damaged by trauma or degenerative disease. Each year more than 650,000 patients worldwide undergo operations in which either part or all of their knee joints is replaced, and the resulting implants typically operate well for 10 or more years. Typically, current designs consist of a metallic component made from a cobalt-based alloy to replace the bearing surfaces of the femur. This femoral prosthesis bears upon an ultra-high molecular weight polyethylene component implanted upon the proximal end of the tibia. Additionally a second polyethylene implant is used to replace the undersurface of the patella so that it slides upon the central region of the metallic femoral implant. To minimize the problem of wear in the joints, the metallic component is polished to a very fine mirrored surface and the bearing surfaces are designed with a high degree of conformity to reduce contact stresses.
One of the major problems with the conventional procedure, however, is that the prostheses are relatively large, and, accordingly, must be inserted through relatively long incisions. Specifically, the large metal component that comprises the femoral implant is generally about four inches wide and about three inches high, which requires a correspondingly large incision for implantation. Such large incisions tend to disrupt the tissues associated with the joint and its joint capsule, requiring long healing and rehabilitation periods after the operation before the patient can return to normal activities. Although surgeons have recognized the desirability of minimizing the size of the incisions, the large size of the prostheses of current design have frustrated attempts to use smaller incisions, e.g., 1-2 inches in length.
U.S. Published Patent Application No. 2003/0158606, to Coon et al., discloses a knee arthroplasty prosthesis wherein a femoral component of a total knee joint replacement is made in more than one piece. The pieces are inserted separately and assembled within the surgical site. The separate pieces of the femoral component are provided with mating surfaces generally formed at an angle to a plane oriented in an anterior-posterior direction and proximal distal direction with respect to the femur. However, the multi-piece prosthesis of Coon is disclosed as requiring a surgical incision of three inches.
Accordingly, a need has continued to exist for a knee joint prosthesis that can be inserted using minimally invasive surgical techniques.